My 1990 XJ-S has Delanair MK3 air conditioning unit.
Recently, the upper rotary blend flap was not working and was locked at cold air position.
I know this problem is caused by the upper servo and the potentiometer fault synchronizing, and the rotary blend flap is twisted by the fault, and then the rotary bread flap is locked.
When the upper flap locked, I can recover the problem by sharp nock the upper servo with screw driver. But the fault happened many time, so I'd change the upper servo and the potentiometer.

My question is another problem in the center vent.
When I set the defrost mode with max heat temperature,

Expecting behavior are
1. The rotary flap not change because of upper rotary blend flap has locked.
2. The center vent flap close and block air stream to center air outlet.

But my air conditioner's behaviors are
1. The rotary flap not change because of upper rotary blend flap has locked.
2. The center vent flap also NOT CLOSE and continue cold air stream to center air outlet.

Dose the center vent flap has any relationship with the rotary flap?

 

Bread?

 

NO, the centre vent is controlled by a vacuum solenoid. It is the rear one on the RH side behind the kick panel at the front of the console.

The default for this solenoid is off which has the centre vent closed. If your solenoid is rusted on then the vent will open as soon as there is vacuum.

My solenoids were rusted from leaking coolant.

Be aware that the connectors for this solenoid are VERY close to the back of the radio, so ensure the insulation on them is in good condition as shorting out WILL cause the AC ECM to fail.

There is a picture of them in here, you can see the one on the left is quite rusty.

Jaguar XJS Restoration : XJS Delanair Mk3 Repair

 

Hi warrjon

Thank you so much for your advice! I understand how run the center vent very clear.
These instructions on your web site are very useful for who has same trouble in their air conditioner.
I should also check the center vent solenoid when I change the upper servo and the potentiometer.

Hi Mark SF

I'm sorry, I made miss spelling on the #1 post (bread > blend).